Grim Necromancer costs 1 extra mana but has +3 health. The fact that this summons mech tokens doesn't matter as much because using your magnetic minions on 1/1 tokens is a pretty weak play. Between these two, Grim Necromancer is the better choice for a token deck.

We've seen this card printed in a million ways, it never works. I don't even need to list them for you to know "big minion surrounded by tokens" is a staple in every other expansion and it never makes it into a deck, just arena.

You may have forgotten, Dr. Boom was a well statted 7 mana 7/7. Ontop of that, the minions he summoned could deal enough damage to kill a minion, and he summoned two of them. This is 3 mana for 4/3, Dr. Boom was a 7 mana 9/9 that dealt 1-4 damage TWICE randomly. You cannot compare these two cards together.

No, I can very clearly see that Dr. Boom is better, and I'm not expecting that Microtech Controller will find a place in the meta. But you said "big minion surrounded by tokens," and that accurately describes Dr. 7.